U.S. patent application number 16/963859 was filed with the patent office on 2021-02-11 for ultrasound imaging system providing needle insertion guidance.
The applicant listed for this patent is KONINKLIJKE PHILIPS N.V.. Invention is credited to Kyong Chang, Shannon Renee Fox, Changhong Hu, James Robertson Jago, Thanasis Loupas.
Application Number | 20210038320 16/963859 |
Document ID | / |
Family ID | 1000005208346 |
Filed Date | 2021-02-11 |
United States Patent
Application |
20210038320 |
Kind Code |
A1 |
Fox; Shannon Renee ; et
al. |
February 11, 2021 |
ULTRASOUND IMAGING SYSTEM PROVIDING NEEDLE INSERTION GUIDANCE
Abstract
An ultrasound imaging system for needle insertion guidance uses
a curved array transducer to scan an image field with unsteered
beams as a needle is inserted into the image field. Due to
differences in the angle of incidence between the radially directed
beams and the needle, echoes will return most strongly from only a
section of the needle. This section is identified in an image, and
the angle of incidence producing the strongest returns is
identified. Beams with this optimal angle of incidence are then
steered in parallel from the curved array transducer to produce the
best needle image. The steep steering angles of some of the steered
beams can give rise to side lobe clutter artifacts, which can be
identified and removed from the image data using dual apodization
processing of the image data.
Inventors: |
Fox; Shannon Renee;
(Everett, WA) ; Hu; Changhong; (Bothell, WA)
; Chang; Kyong; (Mill Creek, WA) ; Jago; James
Robertson; (Seattle, WA) ; Loupas; Thanasis;
(Kirkland, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KONINKLIJKE PHILIPS N.V. |
EINDHOVEN |
|
NL |
|
|
Family ID: |
1000005208346 |
Appl. No.: |
16/963859 |
Filed: |
January 15, 2019 |
PCT Filed: |
January 15, 2019 |
PCT NO: |
PCT/EP2019/050844 |
371 Date: |
July 22, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62620512 |
Jan 23, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 8/0841 20130101;
A61B 2034/2063 20160201; A61B 34/20 20160201; A61B 8/463 20130101;
A61B 8/4488 20130101 |
International
Class: |
A61B 34/20 20060101
A61B034/20; A61B 8/08 20060101 A61B008/08; A61B 8/00 20060101
A61B008/00 |
Claims
1. A method for operating an ultrasonic imaging system for image
guidance of needle insertion in a subject, the method comprising:
transmitting unsteered beams from a curved array transducer in the
probe over an image field in the subject, and thereby obtaining an
ultrasound image of said image field using the unsteered beams;
identifying a peak angle of a transmit beam for producing a peak
magnitude of echo returns from a needle in the image field based on
application of image processing to said ultrasound image;
transmitting a plurality of parallel steered beams at the peak
angle; and displaying a further ultrasound image of the needle in
the image field, the further ultrasound image obtained based on the
steered beams.
2. The method of claim 1, comprising identifying a line of needle
specular reflections in the ultrasound image.
3. The method of claim 2, comprising identifying a brightest point
along the line of needle specular reflections.
4. The method of claim 3, wherein identifying the angle of the
transmit beam comprises identifying the transmit beam which
intersects the line of needle specular reflections at the brightest
point, wherein the identified transmit beam further exhibits the
peak angle.
5. The method of claim 1, wherein displaying the ultrasound image
of the needle comprises displaying a needle guide graphic in the
image.
6. The method of claim 5, wherein displaying the needle guide
graphic comprises displaying a graphic line at a location of the
needle in the ultrasound image.
7. The method of claim 5, wherein displaying the needle guide
graphic comprises displaying needle guide graphic lines on either
side of a location of the needle in the ultrasound image.
8. The method of claim 5, wherein displaying the needle guide
graphic comprises displaying graphic lines at the location of the
needle in the ultrasound image and on either side of a location of
the needle in the ultrasound image.
9. A method for operating an ultrasonic imaging system for image
guidance of needle insertion in a subject, the method comprising:
acquiring image data from an image field in the subject with a
plurality of transducer elements in the probe, the image field
suspected of comprising a needle inserted into the subject;
processing the image data with two different apodization functions
adapted to isolate clutter in the image data; using image data
processed with the two different apodization functions to produce
clutter-reduced image data; and displaying a clutter-reduced
ultrasound image of a needle in the image field.
10. The method of claim 9, wherein processing the image data with
two different apodization functions comprises forming two
ultrasound images from the image data, each using a different
apodization function.
11. The method of claim 10, wherein using image data processed with
the two different apodization functions comprises combining or
correlating image data from the two ultrasound images to produce
clutter-reduced image data.
12. The method of claim 9, wherein processing the image data with
two different apodization functions comprises processing the image
data with complementary apodization functions.
13. The method of claim 12, wherein processing the image data with
complementary apodization functions comprises processing the image
data with apodization functions which affect side lobe artifact
data differently.
14. The method of claim 13, wherein processing the image data with
apodization functions which affect side lobe artifact data
differently comprises using an apodization function which acts as a
notch filter for side lobe or main lobe data.
15. The method of claim 13, wherein using image data processed with
the two different apodization functions comprises combining image
data with both side lobe and main lobe data with image data having
only side lobe or main lobe data.
Description
[0001] This invention relates to medical ultrasound imaging systems
and, in particular, to ultrasound systems which provide image
guidance for insertion of biopsy needles and other invasive
devices.
[0002] Ultrasound image guidance provides a simple and effective
way to insert an invasive device such as a biopsy needle into the
body. The imaging is used to view both the needle and the target
anatomy in the body, and thus the clinician can see and plan the
insertion path to the target as the needle is being inserted. Major
blood vessels and obstacles to smooth insertion such as calcified
tissues can be avoided. But obtaining a clear and complete image of
the needle can be problematic due to the physics of ultrasound.
During the procedure the clinician observes the target anatomy in
the ultrasound image and then inserts the needle adjacent to the
ultrasound probe in a direction aimed toward the target and passing
through the image field of the probe. This path of travel can be at
a relatively steep angle in relation to the ultrasound scanning
beams. While a metallic needle is a strong reflector of ultrasound
and thus presumed to show up clearly in the image, the steep
angular relationship can cause the ultrasound energy to glance off
and travel deeper into the body rather than be reflected directly
back to the probe for image acquisition. Hence, the angular
relationship between the needle shaft and the ultrasound beam
direction can make needle imaging problematic. It is desirable to
design the imaging system so that clear and complete images of a
needle are obtained during insertion, so that the clinician can
constantly know the location and position of the needle in the
body.
[0003] The ultrasound beam angle can pose an additional impediment
to clear and complete needle imaging, which is that returning
echoes can be at steep angles relative to the probe aperture that
give rise to grating lobe (side lobe) artifacts. These artifacts
can appear in the image around the actual needle location in the
image, making it difficult to discern the needle from the
surrounding clutter. It is thus desirable to prevent or eliminate
these clutter artifacts during needle insertion guidance.
[0004] In some aspects, the present disclosure includes methods for
operating an ultrasonic imaging system for image guidance of needle
insertion. The methods can include transmitting unsteered beams
from an ultrasound transducer over an image field in a subject,
identifying a peak angle of a transmit beam for producing a peak
magnitude of echo returns from a needle in the image field,
transmitting a plurality of parallel steered beams at the peak
angle, and displaying an ultrasound image of the needle in the
image field. In certain aspects, the methods can include
identifying a line of needle specular reflections in the ultrasound
image, and/or identifying a brightest point along the line of
needle specular reflections. In some aspects, the identifying the
angle of the transmit beam can include identifying the transmit
beam which intersects the line of needle specular reflections at
the brightest point, wherein the identified transmit beam further
exhibits the peak angle. The displaying the ultrasound image of the
needle can include displaying a needle guide graphic in the image,
which can include displaying a graphic line at a location of the
needle in the ultrasound image. The displaying the needle guide
graphic can include displaying needle guide graphic lines on either
side of a location of the needle in the ultrasound image. The
displaying the needle guide graphic can include displaying graphic
lines at the location of the needle in the ultrasound image and on
either side of a location of the needle in the ultrasound
image.
[0005] In some aspects, the present disclosure can include methods
for operating an ultrasonic imaging system for image guidance of
needle insertion that can include acquiring image data from an
image field within a subject using a plurality transducer elements,
wherein the image field is suspected of including a needle therein,
processing the image data with two different apodization functions
adapted to isolate clutter in the image data, using image data
processed with the two different apodization functions to produce
clutter-reduced image data, and displaying a clutter-reduced
ultrasound image of a needle in the image field. The processing the
image data with two different apodization functions can include
forming two ultrasound images from the image data, each using a
different apodization function. Using image data processed with the
two different apodization functions can include combining or
correlating image data from the two ultrasound images to produce
clutter-reduced image data. Processing the image data with two
different apodization functions can include processing the image
data with complementary apodization functions. Processing the image
data with complementary apodization functions can include
processing the image data with apodization functions which affect
side lobe artifact data differently. Processing the image data with
apodization functions which affect side lobe artifact data
differently can include using an apodization function which acts as
a notch filter for side lobe or main lobe data. Using image data
processed with the two different apodization functions can include
combining image data with both side lobe and main lobe data with
image data having only side lobe or main lobe data.
[0006] In the drawings:
[0007] FIG. 1 illustrates an ultrasound system configured in
accordance with the principles of the present invention.
[0008] FIG. 2 illustrates the angles of incidence between a needle
and unsteered beams from a curved array transducer.
[0009] FIG. 3 is an ultrasound image of insertion of a needle into
a subject at the insertion angle shown in FIG. 2.
[0010] FIG. 4 illustrates acquisition of a needle image by steering
beams in parallel at an optimal angle from a curved array
transducer.
[0011] FIG. 5 is an ultrasound image of a needle with its location
indicated by a needle guide graphic.
[0012] FIG. 6 illustrates a first dual apodization technique which
can be used to reduce clutter arising due to beam steering in
needle guidance imaging.
[0013] FIGS. 7a and 7b illustrate a second dual apodization
technique which can be used to reduce clutter arising due to beam
steering in needle guidance imaging.
[0014] FIGS. 8a and 8b illustrate the sidelobe energy resulting
from use of the two apodization functions of FIGS. 7a and 7b.
[0015] FIG. 9 illustrates the reduction of sidelobe clutter
achieved by a combination of the two apodization functions of FIGS.
7a and 7b.
[0016] FIG. 10 is a flowchart of an ultrasound image guided needle
insertion procedure conducted in accordance with the principles of
the present invention.
[0017] In accordance with the principles of the present invention
an ultrasound system and probe with a convex curved array
transducer are used for needle insertion guidance. The natural
curvature of the array causes its unsteered beams to traverse a
wide sector angle which extends beyond the footprint of the probe
and quickly captures a needle during initial insertion. Images of
the needle are analyzed to determine a point where the angle of
incidence between an ultrasound beam and the needle shaft are best
for needle image acquisition, and a needle image is acquired with
beams steered in parallel from the curved array at the optimized
beam angle. The needle location is indicated in the image with a
needle guide graphic. The optimized beam angle is periodically
updated during the procedure. In accordance with a further aspect
of the present invention, clutter arising due to steep beam
steering angles is reduced by producing images of a scan field with
two different apodization functions, which are then compared or
combined to reduce image clutter.
[0018] Referring now to FIG. 1, an ultrasonic diagnostic imaging
system constructed in accordance with the principles of the present
invention is shown in block diagram form. A convex curved
transducer array 12 is provided in an ultrasound probe 10 for
transmitting ultrasonic waves and receiving echo information. The
curved array transducer is coupled by the probe cable to a
transmit/receive (T/R) switch 16 which switches between
transmission and reception and protects the main beamformer 20 from
high energy transmit signals. The transmission of ultrasonic beams
from the curved array 12 is done under control of a transmit
controller 18 coupled to the T/R switch and the beamformer 20,
which receives input from the user's operation of the user
interface or control panel 38. Among the transmit characteristics
controlled by the transmit controller are the amplitude, phase, and
polarity of transmit waveforms, as well as the focusing and
steering of ultrasound beams effected together with beamformer
control. Beams formed in the direction of ultrasound transmission
may be unsteered (directions orthogonal to the face of the
transducer), or steered at different angles relative to the face of
the array. The echoes received by a contiguous group of transducer
elements referred to as the active aperture are beamformed in the
beamformer 20 by appropriately delaying them and then combining
them to form a coherent echo signal.
[0019] The coherent echo signals undergo signal processing by a
signal processor 26, which includes filtering by a digital filter
and noise reduction as by spatial or frequency compounding. The
signal processor can also shift the frequency band to a lower or
baseband frequency range. The digital filter of the signal
processor 26 can be a filter of the type disclosed in U.S. Pat. No.
5,833,613 (Averkiou et al.), for example. In accordance with one
aspect of the present invention, a clutter processor 50 is coupled
to the signal processor to remove sidelobe clutter arising during
beam steering as described more fully below. The processed echo
signals are demodulated into quadrature (I and Q) components by a
quadrature demodulator 28, which provides signal phase
information.
[0020] The beamformed and processed coherent echo signals are
coupled to a B mode processor 52 which produces a B mode tissue
image. The B mode processor performs amplitude (envelope) detection
of quadrature demodulated I and Q signal components by calculating
the echo signal amplitude in the form of (I.sup.2+Q.sup.2).sup.1/2.
The quadrature echo signal components are also coupled to a Doppler
processor 54, which stores ensembles of echo signals from discrete
points in an image field which are then used to estimate the
Doppler shift at points in the image with a fast Fourier transform
(FFT) processor. For a color Doppler image, the estimated Doppler
flow values at each point in a blood vessel are wall filtered and
converted to color values using a look-up table. The B mode image
signals and the Doppler flow values are coupled to a scan converter
32 which converts the B mode and Doppler samples from their
acquired R-.theta. coordinates to Cartesian (x,y) coordinates for
display in a desired display format, e.g., a rectilinear display
format or a sector display format as shown in FIGS. 3 and 5. Either
the B mode image or the Doppler image may be displayed alone, or
the two shown together in anatomical registration in which the
color Doppler overlay shows the blood flow in tissue and vessel
structure in the image.
[0021] The ultrasound image data produced by the scan converter 32
are coupled to an image processor 30 and a 3D image data memory.
The image processor 30 performs further enhancement, buffering and
temporary storage for display of an ultrasound image on an image
display 40. The 3D image data memory stores image data values at
addresses related to their coordinates in 3D space, from which they
can be accessed for 3D image formation. The 3D image data memory is
coupled to a multiplanar reformatter 44 and a volume renderer 42.
The multiplanar reformatter converts echoes which are received from
points in a common plane in a volumetric region of the body into an
ultrasonic image of that plane, as described in U.S. Pat. No.
6,443,896 (Detmer). The volume renderer 42 converts the echo
signals of a 3D data set into a projected 3D image as viewed from a
given reference point as described in U.S. Pat. No. 6,530,885
(Entrekin et al.) The 2D or 3D images produced from 3D image data
are coupled to the image processor 30. A graphic display overlay
containing textual and other graphic information such as patient ID
is produced by a graphics processor 36 for display with the
ultrasound images.
[0022] FIG. 2 illustrates an image field 60 which is scanned by
unsteered beams 62 transmitted and received by a curved array
transducer. The beams are unsteered because their directions are
determined by the curved geometry of the array; each beam is
directed normal to its point of origin along the face of the array.
In beam formation, unsteered beams are formed by equally weighting
echoes received at symmetrical locations of the active aperture on
either side of the point of origin. The beams have a symmetrical
weighting profile in the beamformer. The same symmetrical weighting
profile can be used to form each beam along the array, with the
different angular directions of the beams provided by the
geometrical array curvature. The natural curvature of the array
thus causes each beam 62 to be directed at a different angle across
the image field, thus scanning a sector-shaped field 60. This is
advantageous for needle insertion imaging, as only a single
weighting table needs to be loaded into the beamformer for scanning
and echo formation along each different beam direction. The broad
sector image field is advantageous for needle insertion imaging,
since the needle is inserted into the body at the side of the
probe, and in line with the scan plane. The needle is quickly
acquired at the edge of the wide image, as it will begin to
intersect beams at the side of the sector after just a few
millimeters of insertion.
[0023] But the angle of the inserted needle relative to the beam
angles will cause different degrees of echo detection from
different transmit beams depending on the angle of incidence of the
beams impinging upon the needle. In the illustration the beams
intersecting the needle 70 before and after the central darkened
section 72 are at non-orthogonal angles relative to the needle
shaft. Echoes from these beams will scatter in directions away from
the beam path, and less of their energy will return to the array
elements. The darkened beams on either side of beam 64 are more
orthogonal to the shaft of needle 70, causing more of their energy
to be reflected back directly to the array. The beam 64 is most
optimal as it is nearly orthogonal to the needle at its point of
intersection and echoes from this beam will most strongly return to
the array from the specular reflecting needle. Thus the section 72
of the needle which produces these stronger echo returns will
appear most distinctly in the ultrasound image, as clearly shown in
the actual ultrasound image 66 of FIG. 3. (This image is shown with
black-white display reversal for better illustration.)
[0024] In accordance with the present invention, the ultrasound
system includes a needle location processor 46 which identifies the
distinct needle section 72 in the ultrasound image 66, and
particularly the angle of the most optimal beam 64. The needle
location processor uses image processing to search for and identify
the straight line of strong echoes from needle section 72 in the
image. This can be done using image processing techniques such as
Hough transforms, Radon transforms, first- and second-order
directional texture analysis, or heuristic criteria such as maximum
brightness analysis. When this echo return section is identified in
the image, the point along the section of the strongest echo return
denotes the point where the optimal unsteered beam intersects the
needle, and the identity of the beam is thus determined by simple
geometry. With beam 64 thereby identified as the unsteered beam
with the optimal angle for imaging the needle most strongly, the
needle location processor commands the transmit controller 18 and
beamformer 20 to transmit and receive steered beams from the array
12, all steered at the identified optimal angle of beam 64. This is
shown in FIG. 4, where the array 12 is shown transmitting beams 64'
. . . 64 . . . 64'', all transmitted and received at the same angle
relative to the needle 70, an angle which is nearly orthogonal to
the needle. Also shown for comparison are arrows 62 depicting
unsteered beam angles from the array 12. The steered beams 64' . .
. 64 . . . 64'' are seen to emanate from the same points along the
face F of the array as the unsteered beams, but are steered by
phased operation at different respective angles relative to the
face F of the array which causes them to all be directed in
parallel, and to impinge upon the needle at an orthogonal or nearly
orthogonal angle. Imaging the needle with these parallel steered
beams will produce relatively strong echo returns from the needle
70, and a sharper, clearer appearance of the needle in the
ultrasound image.
[0025] Scanning with parallel steered beams from a curved array is
a nonobvious use of a curved array. This is because a curved array
has an inherent preferential radial scan pattern due to its curved
geometry. A standard flat linear array, by comparison, has no
inherent radial scan pattern. Its flat geometry has made it the
array of choice for linear as well as phased beam steering.
So-called "steered linear" scanning has long been performed by
phased operation of flat linear arrays for color Doppler imaging,
as exemplified by U.S. Pat. No. 5,014,710 (Maslak et al.), as has
phased sector scanning. One skilled in ultrasonic imaging would
choose a curved array specifically to take advantage of its natural
radial scan pattern, not for use in steered parallel beam scanning.
Not only is the curved array geometrically unsuited for this mode
of operation; phased steering of beams from a curved array quickly
gives rise to side lobe artifact clutter due to steep beam steering
angles, as discussed in detail below.
[0026] When the needle location processor 46 has operated as
described to locate the needle in the ultrasound image as just
explained, it further commands the graphics processor 36 to overlay
the ultrasound image 66 with a needle location graphic as shown in
FIG. 5. Needle guidance systems of the prior art have generally
positioned needle location graphics over the location of the needle
itself, as shown by the dotted graphic 80 which is positioned over
the needle location in the body. This can pose a difficulty, as the
image of the needle is obscured by the graphic. Often, the
clinician would prefer to have the needle in the image
unobstructed, particularly around the needle tip, which the
clinician is usually focused on most intently to guide the
insertion. A preferred graphic which does not obstruct the needle
in the image has graphic lines 82a and 82b which frame the image of
the needle between them. The graphics 82a, 82b quickly identify the
needle location for the clinician without obscuring the image of
the needle or the needle tip. Some clinicians may prefer to use
both graphics, with the lines 82a, 82b encompassing the needle
location and a lighter or broken line graphic 80 specifically
identifying the shaft of the needle in the image.
[0027] As needle insertion progresses, the direction of insertion
can change as the clinician manipulates the needle to avoid
piercing blood vessels or work around hard substances in the body.
Since the needle orientation can change due to needle manipulation
or probe movement, the image processing and optimal beam angle
identification and beam steering are repeated periodically by the
needle location processor 46, updating the steering angle of beams
64, 64' as needed to maintain the clearest image of the needle as
can be afforded by the procedure.
[0028] An ultrasound array, like a radio antenna, exhibits an
energy profile of the ultrasound energy transmitted or received by
the array. This antenna pattern for an ultrasound array is known as
a lobe pattern. The pattern has a main or central lobe which
axially aligns with the beam direction, and side lobes which can
also be sensitive to off-axis echo reception. In most instances,
the clinician would prefer a strong, narrow main lobe in the beam
direction, and virtually nonexistent side lobes. This is because
energy received in side lobes in the image field can result in the
production of artifacts in the image during beamformation, clutter
which can obscure the image of the needle. The beamformer is
programmed on the assumption that all energy is being received from
along the beam axis. Off-axis energy received from the side lobes
will be undesirably beamformed and manifest itself as artifacts in
the resultant image. Side lobe clutter artifacts are prevented by
using a probe with an element pitch (center-to-center spacing)
which is less than half of the ultrasound frequency wavelength.
When the beams of the curved array are unsteered, a half-wavelength
element pitch will avoid the appearance of side lobe clutter. But
when beams are steered at increasing nonorthogonal angles to the
face of the array, side lobes become larger and the likelihood of
side lobe artifacts increases, particularly in the case of a curved
array where the array curvature causes the steered angles at the
face of the array to be steeper than would be the case with a flat
linear array. In FIG. 4 it is seen that the outermost needle
imaging beams 64' and 64'' are at significant nonorthogonal
steering angles relative to the face F of the array 12, and these
steeper steering angles can be a source of side lobe image clutter.
In accordance with a further aspect of the present invention, side
lobe clutter is reduced by a clutter processor 50 in the ultrasound
system. The clutter processor 50 operates by forming two ultrasound
images from the echoes produces from a scan of the image field,
each using a different apodization function. The pixel values of
the two differently apodized images are combined to reduce side
lobe clutter artifacts in the final image.
[0029] One set of apodization functions for clutter removal is
shown in FIG. 6. At the bottom of the drawing is an array 12 of
transducer elements e, extending in a direction y. Shown above the
array 12 in spatial correspondence are two different apodization
functions 92 and 92. One apodization function is used when
beamforming the echo signals received from the image field to form
a first image, and the other apodization function is used when
beamforming the same echo signals to form a second image. It is
seen that apodization function 92 weights the signals from two
adjacent elements with a weight of one, then the signals from the
next two elements with a weight of zero, then the next two signals
with a weight of one, and so on. The apodization function 94 is the
inverse, with the same alternation of one and zero weights across
the aperture. The beamformed echo signals of the two images are
amplitude detected, producing pixel values for the two images.
Pixel values at the same spatial location in the two images are
then compared or correlated. If the correlation of the two values
is high, such as greater than 50%, one or both of the values are
used for that pixel value in the resultant image. If the
correlation of the two values is relatively low, such as less than
50%, the values are omitted from the image. That is because the
main lobe signals processed by the two complementary apodization
functions will be approximately the same, whereas signals from the
side lobes on either side of the main lobe in the two images, the
side lobes which are the greatest contributors of clutter, will be
of opposite polarity and de-correlated. Thus, side lobe clutter is
reduced in the resultant image. Since this processing is all done
on a single image acquisition, there is no adverse effect on the
frame rate of display. And since this clutter reduction processing
uses amplitude detection, the resultant pixel values can be
directly processed into a B mode image by the B mode processor
52.
[0030] Preferred apodization functions for clutter reduction of
needle images are shown in FIGS. 7a and 7b. The graphs of these two
drawings are plotted as voltage weighting, v, against distance from
the center of the ultrasonic transducer array, y. The graph 410 of
FIG. 7a shows an example of a first apodization function in the
form of a rectangular apodization function. This apodization
function results in signals from all of the elements of the
transducer array receive an equal weighting such as one. The
results of applying this function to the received echo data are
shown in FIG. 8a.
[0031] FIG. 8a shows a plot 500 of magnitude, measured in dB,
against steering angle .theta.. The plot depicts the summation of
all of the echo signals received by each transducer element of a
transducer array, across all of the steering angles within the
field of view of the array. More specifically, the plot shows the
main and side lobe response in image data beamformed using the
first apodization function 410 shown in FIG. 7a. This is the
response characteristic of a standard unapodized B-mode ultrasound
image, which has a high intensity response at a steering angle of
0.degree. 510, the main lobe response 520. Signals from a steering
angle of 0.degree. arrive coherently at the transducer array and
form the main lobe response of an image using uniform apodization
function 410. Due to spatial resolution limitations, the main lobe
520 has a finite width that includes a small range of angles either
side of zero degrees. Image data with this characteristic also
includes multiple signals of diminishing intensity spreading out
from the main lobe, the side lobes 530. The side lobes are the
response of signals with a steering angle outside of the range of
the main lobe. Constructive and destructive interference effects at
different angles create the peaks and troughs in the side lobes.
The side lobes contribute the clutter in an ultrasound image,
whereas the main lobe provides the desired signals from the
ultrasound image target.
[0032] The second graph 420 of FIG. 7b shows an example of a second
apodization function in the form of a reciprocal function, such as
y=1/x, which is used to introduce a null point in the image data
response as illustrated by FIG. 8b. When this notch filter is
applied as a pass filter to the lobe characteristic 500, signals
from the main lobe of the beampattern of the array receive a high
weighting, which decreases exponentially towards signals from the
more lateral side lobes. The results of applying this function to
the received echo data are shown in FIG. 9. The shapes of the
apodization functions used may be designed by the user of the
ultrasound system or may be preloaded onto the system and selected
by the user to perform a desired function. Once the shape of an
apodization function has been selected or designed, it may be
adjusted through a single control parameter. This parameter is a
scaling factor, k, which may be empirically determined by the user
through the use of the ultrasound system.
[0033] Linear acoustics dictates that the ultrasound beampattern is
equivalent to the Fourier transform of the apodization function
used. This relationship provides a tool for analysis and
beampattern design. More specifically, it is possible to design the
apodization function to achieve a desired beampattern. For example,
the image data produced by use of the apodization function 420 will
exhibit a sharp null at the main lobe location and a decreased
amplitude at off-axis steering angles, as shown in FIG. 8b. The
Fourier transform relationship between the apodization function 420
and the beampattern of the second image data can be used to discern
what type of apodization function should be used to achieve the
desired beampattern.
[0034] By applying the reciprocal second apodization function 420
to the echo signal data, a null 560 is generated at the same
steering angle as the main lobe 520 of the image data processed
using apodization function 410. In this example, the second
apodization function 420 is acting as a notch filter; however,
depending on the application, many different shapes of apodization
function may be utilized.
[0035] FIG. 9 shows a plot 600 depicting a superposition of the
plots from FIGS. 8a and 8b, which depict the image data resulting
from use of the first and second apodization functions 410 and 420,
respectively, for an image pixel. By comparing pixels of the first
and second images processed by the apodization functions, the
minimum signal magnitude across the steering angles can be found.
This is highlighted by dashed lines 630 of the side lobe response.
Signals of the desired main lobe 610 fall in the notch of the
characteristic of the second apodization function 620. In this way,
the clutter signals of the side lobes 630 are selected and isolated
from the signals of the main lobe 610. The unwanted values from the
side lobe response 630 are then subtracted from the image data
obtained using the first apodization function 410 with the response
shown in FIG. 8a. The result is signals mainly returned from the
main lobe response 520, and the signals of the side lobes 530 of
the lobe pattern have been substantially eliminated, meaning that
the resulting signal used for imaging is primarily signals from the
main lobe response of the lobe characteristic. In this way,
sidelobe clutter is substantially removed from the ultrasound
image.
[0036] The shape of the second apodization function, shown in graph
420 of FIG. 7b, may be altered to change the width of the null
function 560 in the second image data. In this way, the angular
spread of the remaining signals may be controlled. By reducing the
width of this notch function, the spatial resolution of the final
ultrasound image may be increased.
[0037] An ultrasound image-guided needle insertion procedure in
accordance with the present invention is outlined in FIG. 10. A
clinician begins the procedure by positioning a curved array
transducer probe on the body of a subject, manipulating the probe
until the target anatomy for the procedure is in the field of view.
The target anatomy may be a cyst which is to be biopsied using a
needle, for instance. With the target anatomy in view in the
ultrasound image, the clinician starts inserting the needle in-line
with the plane of the image, as stated in step 102. As the
insertion proceeds, the curved array transducer transmits unsteered
beams over the field of view to image the field and capture the
insertion of the needle as stated in step 104. In step 106 the
needle location processor of the ultrasound system identifies the
line of specular needle reflections in the image, where the
radially directed beams from the curved array are intersecting the
needle around the most favorable angle. In step 108 the needle
location processor identifies the brightest point along the needle
reflection line, which identifies the angle of the transmit beam
which produced that bright point as stated in step 110. The needle
location processor then causes the transmit controller to control
the curved array transducer to transmit parallel steered beams
toward the needle at the identified beam angle as stated in step
112. Scanning with the parallel steered beams produces the
strongest image of the needle, and a needle guide graphic is
displayed with the image in step 114, preferably on either side of
the location of the needle in the ultrasound image. Clutter
reduction may then be performed using one of the dual apodization
processing techniques explained above.
[0038] It should be noted that an ultrasound system suitable for
use in an implementation of the present invention, and in
particular the component structure of the ultrasound system of FIG.
1, may be implemented in hardware, software or a combination
thereof. The various embodiments and/or components of an ultrasound
system, for example, the needle location processor 46 and the
clutter processor 50, or components and controllers therein, also
may be implemented as part of one or more computers or
microprocessors. The computer or processor may include a computing
device, an input device, a display unit and an interface, for
example, for accessing the Internet. The computer or processor may
include a microprocessor. The microprocessor may be connected to a
communication bus, for example, to access a PACS system or the data
network for importing images. The computer or processor may also
include a memory. The memory devices such as the 3D image data
memory 48 may include Random Access Memory (RAM) and Read Only
Memory (ROM). The computer or processor further may include a
storage device, which may be a hard disk drive or a removable
storage drive such as a floppy disk drive, optical disk drive,
solid-state thumb drive, and the like. The storage device may also
be other similar means for loading computer programs or other
instructions into the computer or processor.
[0039] As used herein, the term "computer" or "module" or
"processor" or "workstation" may include any processor-based or
microprocessor-based system including systems using
microcontrollers, reduced instruction set computers (RISC), ASICs,
logic circuits, and any other circuit or processor capable of
executing the functions described herein. The above examples are
exemplary only, and are thus not intended to limit in any way the
definition and/or meaning of these terms.
[0040] The computer or processor executes a set of instructions
that are stored in one or more storage elements, in order to
process input data. The storage elements may also store data or
other information as desired or needed. The storage element may be
in the form of an information source or a physical memory element
within a processing machine.
[0041] The set of instructions of an ultrasound system including
those controlling the acquisition, processing, and transmission of
ultrasound images as described above may include various commands
that instruct a computer or processor as a processing machine to
perform specific operations such as the methods and processes of
the various embodiments of the invention. The set of instructions
may be in the form of a software program. The software may be in
various forms such as system software or application software and
which may be embodied as a tangible and non-transitory computer
readable medium. Further, the software may be in the form of a
collection of separate programs or modules such as a needle
location module, a clutter module, a program module within a larger
program or a portion of a program module. The software also may
include modular programming in the form of object-oriented
programming. The processing of input data by the processing machine
may be in response to operator commands, or in response to results
of previous processing, or in response to a request made by another
processing machine.
[0042] Furthermore, the limitations of the following claims are not
written in means-plus-function format and are not intended to be
interpreted based on 35 U.S.C. 112, sixth paragraph, unless and
until such claim limitations expressly use the phrase "means for"
followed by a statement of function devoid of further
structure.
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